Thesis/Objective – This article presents the results of a quantitative comparative analysis of the activity of 65 Polish public university libraries on a social media platform known as Instagram between 2015 and 2023. The aim of the study was to assess the use of Instagram by academic libraries and to evaluate the popularity of the content shared by these institutions (including the number of posts shared and user reactions to them). Research methods – The commercial online tool Fanpage Karma, a social media monitoring service, was used to collect data from individual fanpages. This service also facilitated the processing of the collected data for statistical purposes. Data were gathered separately for different types of libraries. The critical analysis of the relevant literature and bibliographic sources was also conducted. Results/Conclusions – The results showed that only 33 out of 65 public academic libraries use Instagram in their everyday work. This activity is generally independent of the library type. The social media platform in question is present in various types of libraries. In some cases, Instagram complements communication via Facebook, particularly in the libraries which are most active on social media. It is worth noting that two libraries use Instagram as their sole social media platform. The highest number of posts was published by university libraries – and those posts received most user reactions.